单项选择题

A."岂直规规治疾方术已哉"的"直"
B."苞无穷,协惟一"的"惟"
C."第以人心积习既久"的"第"
D."众药聚门,适足多疑"的"适"
E."即病者亦但知膏肓难挽"的"但"